1. Field of the Invention
The invention refers to a needle assembly, consisting of a plastic cannula with a hollow hub at its distal end, a steel needle adapted for insertion into the plastic cannula and having a ground tip and a needle head adapted for being detachably coupled with the hollow hub, and a tube-like protecting cap for the elongated parts.
2. Description of the Related Art
In a needle assembly of this kind, the pointed steel-needle tip protruding beyond the blunt end of the plastic cannula effects the puncture of a blood vessel. After withdrawal of the steel needle, the plastic cannula serves as an in-dwelling cannula which remains in the blood vessel and has its hollow hub connected to a transfer device for infusion or transfusion of liquids. The free steel needle is disposed of. To prevent the medical staff and waste disposal personnel from being infected by punctures, e.g., with hepatitis or AIDS, it is necessary that the ground tip of the comparatively large-gauged steel needle be protected by attaching the protecting cap when thrown away. The precondition for such a protection, however, is a secure fastening of the protecting cap to the steel needle arrangement. This causes certain problems. When the needle assembly is ready for use, the open end of the protecting cap is clampingly plugged over an adapted extension of the hollow hub of the plastic cannula. The other end of the protecting cap, which can be open or closed by a bottom, extends for a length beyond the ground tip of the steel needle so that the steel needle is covered. If the open end of the protecting cap is clampingly plugged over the extension of the needle head, in a needle assembly having a short hollow hub of the plastic cannula, then the protecting cap will fit onto the withdrawn steel needle without being considerably elongated. However, the stability of this assembly depends on maintaining very narrow tolerances during production of the parts. Thus, even the basically simple protecting cap becomes an expensive special part. In needle assemblies in which the hollow hub of the plastic cannula is provided with fixing plates for attachment on the skin of the patient, there is the disadvantage that the protecting cap is considerably shorter than the steel needle. Thus, after being withdrawn from the plastic cannula, the steel needle cannot be assembled with the extension of the needle head forming a connection with the protecting cap. To allow plugging of the protecting cap onto the steel needle after puncture so that the needle can be disposed of, the protecting cap must have an additional length in the range of the longitudinal extension of the fixing plates. This, however, increases the packing and transport volume of such needle assemblies by about 20 percent (20%), thus raising the costs.